One would think that calculating a basic political statistic like voter turnout
would be straightforward. It's not. Consider the many different ways one
could go about defining the concept of voter turnout:

V/RV: Number of voters as a percent of registered voters.

V/VAP: Number of voters as a percent of the voting age
population.

V/VAC: Number of voters as a percent of the number of voting age
citizens.

V/VEP: Number of voters as a percent of the population eligible
to vote.

The registered voter turnout statistic (V/RV) is of concern only in very
specialized applications; when using it note the problematic nature of the
concept: registration standards vary from state to state, some states have same
day registration and states and localities vary greatly in terms of how often
they purge voters who may have moved or died from the voter registration rolls.

The most common voter turnout statistic is the measure of
voters as a percent of the voting age population. This is especially useful as a
measure related to characteristics of democratic society in a political system.
See International
data. Especially when comparing US states, measuring citizen
voting percentages may be a more valid measure of political participation, but
it depends on what one means by political participation. Whichever concept
one is trying to measure, however, there are omplications.

Counting the voters.

How, for example does one count the number of voters? Surprisingly, not
all American states actually count the number of people who vote in elections. The
most common solution is to count the number of votes cast for president
(in presidential election years) and the number of votes cast for the house of
representatives in congressional election years. The 2000 presidential
election provided a stunning reminder that not all voters who turned out cast
votes for president or had their votes counted as having been cast. In
Congressional election years this is an even greater problem; especially because
some Congressional elections are not contested, a significant number of voters
probably do not cast votes for Congress. In addition the "votes cast"
measure has a significant disadvantage: the data are derived from local election
records which are reported, in most cases, to the state secretaries of state
(and then compiled by the non-governmental Congress Quarterly). Except for
a few Southern states that are required to report the race of registered voters,
election officials collect almost no other demographic data on their voters.
Thus it is not possible to use this statistics to measure voter turnout for
different racial and ethnic groups, different ages, or any demographic category
other than geographic residence.

Potentially a better measure of the number of voters cast is derived from the
November
Current Population Survey (CPS) conducted by the Census Bureau in
presidential and congressional election years. The monthly CPS is based on
interviews of a sample of approximately 55,000 households, providing for a
sampling error of something less than half a percent. Because the survey
also includes information on a wide range of demographic characteristics
(citizenship, age, race, income, but not religion or political party). The
Census Bureau is careful to always refer to this statistic as a measure of
reported voting (RV), implicitly acknowledging that not everyone answering
the survey may be telling the truth. For the 2000 election, the votes cast
measure (CQ /VAP) indicated that 51.2% of the voting age population cast votes
that were counted, while the CPS measure (CPS /VAP) indicates that 54.7%. This
would indicate that approximately 3.5% of the voting age population either:

voted, but not for president,

voted for president, but their votes were not counted or,

did not vote, but told the Census Bureau that they did.

The American
National Election Survey (NES) conducted by the University of Michigan is a
frequent source of voting participation data used in political science research
and is conducted before and after each presidential and congressional election.
Based on a survey of approximately 1,500 persons (sampling error about 2.5%),
the NES data consistently report a much higher level of voter turnout -- 72.7%
in the 2000 election. This would indicate that there is something wrong
with the University of Michigan sample (the NES response rate fell to 52% for
the 2000 election while the CPS maintains a response rate higher than 90%) or
that people are more likely to lie to the university pollsters than they are to
the Census Bureau. The advantage of the NES data is that the survey
includes a great many other questions that the Census Bureau does not ask.
If you want to compare the voter turnout rates for Democrats and Republicans,
different religions or people who have different opinions on different social
issues, the NES is the best source of data (see
some of these data here). Of course, nobody knows how much respondents
lie on those other questions.

Deciding on the denominator in the turnout equation also
presents difficulties.......

Figure E1: Five Measures of Turnout

Things to watch out for:

Although the US has a lower record of voter turnout that
most other countries, Americans have more elections and vote for more elected
officials than any other country. Since 1945, France and England have each had
15 national elections, the US has had 26. Few parliamentary democracies
have elections as often as every two years, few Democracies have primary
elections (fewer, still, have open primaries). The practice of holding
elections for offices such as County treasurer, County recorder, County
assessor, and County coroner (as is the case in Illinois) is a peculiarly
American phenomenon.

When interpreting the time series trends in American voter
turnout, be aware that much of the post-1972 drop in voter turnout had to do
with the 26th Amendment which provided 18 year olds the right to vote (a few
states allowed persons under 21 to vote before 1972). This accounts for
the decline from pre-1972 to post 1972 and most of the decline in voter turnout
since 1972, since the younger voters less likely and increasingly unlikely to
vote.